1. Field of the Invention
The present invention relates to bending machines and, in particular, to bending machines which utilize expandable controlled pressure devices to distribute the bending pressure uniformly over the surface of the work material.
2. Description of the Prior Art
Sheet metal processing utilizing machines that automatically bend sheet metal have been available in the prior art for many years. For example, the Amada Company, Ltd., Kanagawa, Japan manufactures machines of this type which have many enhanced features such as sectionalized punch holders and a lower beam that moves on pre-loaded bearing guide blocks rather than on conventional friction guides. Although these and similar machines have significantly advanced sheet metal processing technology, one of the problems frequently encountered is that the pressure applied to the work material is not uniform, resulting in fabricated parts which do not conform to the required shape. The non-uniformity in applied pressure is due, in part, to the use of fluid controlled hydraulic pistons to move the lower beam into contact with the tool containing portion of the machine.
In addition, if a piston fails because of leaking in the "O"ring, the entire bending process will be interrupted until the failed piston is repaired or replaced, increasing production costs.
U.S. Pat. No. 4,202,264 to Hausman discloses the use of an inflatable pressure container to transfer power to a ram in a hydraulic press without the necessity of using conventional piston seals and gaskets, and in addition, which provides a uniform pressure over its operating surface.
What is desired is to provide a bending machine which avoids the disadvantages inherent in using a hydraulic cylinder based pressure system by utilizing instead the uniform pressure capabilities of an inflatable pressure container.